1. Field of the Invention
The present invention relates to an aligning-positioning mechanism and an aligning-positioning method for positioning a pipe or a shaft to be arranged in a circular hole.
2. Description of the Related Art
In the related art, there are many mechanical parts, which need positioning of a pipe or a shaft in a circular hole. FIG. 5 is a schematic top plan view showing the state, in which a pipe 112 of a circular section is concentrically positioned in a circular hole 111 formed in a block 110 and in which a plate 113 is fitted without any clearance from the hole 111 and the pipe 112 in a space of a torus shape formed by the hole 111 and the pipe 112.
This constitution is disclosed in JP-A-2003-94158 as such a nozzle device, for example, in a metallic injection molding machine as minimizes the unnecessary portions other than the product thereby to lower the cost for the metal machining. FIG. 6 is a schematic section showing one example of the metallic injection molding machine of the related art having the constitution of FIG. 5.
The metallic injection molding machine includes a heating cylinder 202 having a heater 221 disposed on its outer circumference portion, and an extended nozzle 203, which is mounted on the leading end of the heating cylinder 202 and which can be inserted into the mold. A positioning plate 241 is fitted in a hole 243 formed in a stationary mold 204. The leading end portion 232 of the extended nozzle 203 is fitted in the positioning plate 241 fitted in that hole 243.
The leading end portion 232 of the extended nozzle 203 is inserted in the hole formed by the positioning plate 241, and the outer circumference clearance of the leading end portion 232 is sealed up due to the thermal expansion difference between the positioning plate 241 and the leading end portion 232 thereby to prevent the outflow and burst of molten metal.
Against a taper portion 242 formed at the stationary die 204, there abuts a taper portion 231, which is formed at an intermediate portion of the extended nozzle 203 thereby to receive the touching force of the metallic injection molding machine.
Moreover, the positioning plate 241 is mounted on the stationary die 204 from the side of a movable die of the stationary die 204, on which a product ejecting mechanism 251 is disposed.
In this constitution, it has to be avoided with a view to preventing the outflow and burst of the molten metal that a clearance more than that for the smooth fitting is formed either between the stationary die 204 and the positioning plate 241 or between the positioning plate 241 and the leading end portion 232 of the extended nozzle 203. On the other hand, the shape of the positioning plate 241 is seriously influenced by the relative positions of the hole 243 and the leading end portion 232.
Here: the hole 243 of FIG. 6 corresponds to the hole 111 in FIG. 5; the leading end portion 232 of FIG. 6 corresponds to the pipe 112 in FIG. 5; and the positioning plate 241 of FIG. 6 corresponds to the plate 113 in FIG. 5.
In the constitution thus far described, the shape of the positioning plate 241 is influenced by the relative positions of the hole 243 and the leading end portion 232. In order to avoid preparations of a plurality of positioning plates 241 for the individual eccentricities of the leading end portion 232 from the hole 243, therefore, it is preferred that the leading end portion 232 is completely concentric to the hole 243.
In the metallic injection molding machine, however, due to errors at the time of assembling the heating cylinder 202 or due to the curvature of the heating cylinder 202 by the thermal stress to be caused by the circumferential temperature difference of the heating cylinder 202, more or less misalignment occurs on the center of the leading end portion 232 of the extended nozzle 203 mounted on the leading end of the heating cylinder 202. Therefore, the metallic injection molding machine is usually equipped with the nozzle aligning mechanism, which is mostly intended to adjust the deviation at the unit of several millimeters. On the other hand, the maximum clearance permitted to prevent the intrusion of the molten metal from the clearance between the leading end portion 232 and the positioning plate 241 is several tens micrometers. In other words, it is seriously difficult to align the leading end portion 232 and the hole 243 so that the molten metal may be prevented from intruding into the clearance between the leading end portion 232 and the positioning plate 241 by using the ordinary nozzle aligning mechanism.
Therefore, the positioning for making concentric the hole 243 to be fitted on the outer circumference of the positioning plate 241 of the stationary die 204 and the leading end portion 232 of the extended nozzle 203 is performed by fitting between the taper portion 231 formed at the intermediate portion of the extended nozzle 203 and the taper portion 242 formed at the stationary die 204. This makes it necessary to work the taper portion 231 on the side of the extended nozzle 203 and the taper portion 242 on the side of the stationary die 204 extremely precisely. A high sizing precision is also required on the components from the individual taper portions 231 and 242 to the fitting portion between the leading end portion 232 and the positioning plate 241. These being considered, however, it is seriously difficult and not practical to keep the concentricity between the hole 243 and the leading end portion 232 always within a range of several ten micrometers.
As countermeasures, there has been adopted a method for enlarging the clearance between the hole 243 of the stationary die 204 and the outer circumference of the positioning plate 241. By mounting the positioning plate 241 in the hole 243 of the stationary die 204 with an offset of the eccentricity of the leading end portion 232, more specifically, the positioning plate 241 and the leading end portion 232 are fitted.
According to this method, however, there is established between the stationary die 204 and the positioning plate 241 a clearance which is the sum of the inherent clearance and the eccentricity of the leading end portion 232 from the hole 243. Therefore, the molten metal does not flow out to the outside of the die but intrudes into the clearance between the stationary die 204 and the positioning plate 241. As a result, the positioning plate 241 cannot be disassembled from the stationary die 204, or a molding 206 may be left in the stationary die 204 when the die is opened during the molding operation.
In order to avoid the troubles due to the intrusion of the molten metal, the constitution is modified, as shown in FIG. 7, such that the taper portion 231 formed at the intermediate portion of the extended nozzle 203 is made of a bushing 233 different from the extended nozzle 203 thereby to form a clearance between the bushing 233 and the extended nozzle 203. Alternatively, the constitution is modified, as shown in FIG. 8, such that a contacting portion 250 between the intermediate portion of the extended nozzle 203 and the stationary die 204 is formed into a vertically abutting shape so that the alignment may be done by the aforementioned nozzle aligning mechanism. However, this adjusting work is difficult, as has been described hereinbefore, and the working time period for preparing the run may be long.